Photonic integrated circuits (PICs) integrate many optical functions on a single chip. These circuits require a means of connecting the individual light processing elements inside the circuits to each other. Waveguides, whose operation is based on refractive index contrast, are typical elements that transfer light from one element to the other in optical circuits.
Waveguides that are narrow compared the wavelength of the light in the waveguide are typically used in PICs because they carry a single well-defined mode, a property that enables direct connection to optical signal processing and networking elements. Narrow waveguides can also be bent without incurring high optical losses, allowing flexibility in layout. However, narrow waveguides have typically high propagation losses due to the interaction of the optical mode with the waveguide surface. On the other hand, waveguides that are wide compared to the wavelength of the light in the waveguide have low propagation losses for the fundamental mode and are better suited to span larger distances across the chip containing the PIC. However, these waveguides cannot interface easily to other optical components, nor can they be bent with low optical loss due to mode conversion in the bent sections.
Furthermore, typical narrow waveguide bend designs have intrinsic mismatch losses due to the offset and asymmetry of the optical mode inside a bend. Such mismatch losses can be mitigated by physically offsetting the two waveguides in the plane of the bend but cannot be fully eliminated by traditional means in high index contrast systems.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.